Iterative telegraph system



g. 11, 1936. I R, BOWN f 2,050,265

r ITERATIVE TELEGRAPH SYSTEM l Filed July 14, 1935 I 2 Sheets-Sheet 1 o oo oo 1 ce? ou o o o o o [si Band AMP-gzfld Detefar [TY/fer Defecfor Amp.

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R. BOWN ITERAT IVE TELEGRAPH SYSTEM Filed July 14, 19:55

2 Sheets-Sheet 2 A {TORNEY Patented Aug. 11, 1936 UNITED STATES PATENT OFFICE ITERATIVE TELEGRAPH SYSTEM Application July 14, 1933, Serial'No. 680,486

7 Claims.

This invention relates to a system for preventing errors in printing telegraphy due to noise or transmission variations. More particularly it relates to a system for repeating signals automatically at intervals and automatically comparing the received signals with each other to eliminate erro-rs. Y

In radlotelegraphy by older methods such, for example, as manual sending and aural receiving it has been customary to send each word twice or three times when necessary to overcome the veffects of static in obliterating occasional Words and characters. Systems have been proposed lfor applying this arrangement to printing telegraphy by repeating each character one or more times and selecting for record at the receiving end the character indicated by the summation of the repeated signals. The present invention provides a system whereby this principle is further extended to mitigate not only the effects of noise but also the effects of fading. y The fading of radio signals often occurs at such a slow rate that repetition of signals by the ordinary method is ineffective since all repetitions are lost in a fade out. An object of the present invention is to lengthen the intervals between repetitions to avoid this diiliculty. The rates of fading, while sometimes regular for considerable periods, may be widely different at other periods, thus any fixed repetition interval may at times synchronize with the fading rate and cause all repetitions to be lost. A further object of this invention is to provide means for changing the repetition interval from time to time and means for employing simultaneously two or more different repetition intervals. Another object is to provide means automatically to reject from consideration signals too weak to be accurate or signals definitely obliterated by static or noise.

This invention will be fully understood from the following description when read in connection with the accompanying drawings of which Figure 1 illustrates transmitting apparatus, Fig. 2 illustrates receiving apparatus, Fig. 3'il1ustratesa modication of the invention, and Fig. 4 shows in greater detail the modification shown in Fig. 3.v

These illustrations show how the invention may be practiced using many of the devices now common in printing telegraph systems. Obviously simpler mechanisms more specifically designed for the purpose could be employed without departing from the essential principles of the invention.

This illustration of the invention as shown in (Cl. Z50-8) the appended drawings provides that messages be sent from perforated tape which passes through three or more contro-l senders working in rotation, each sender repeating the character at a time (greater than one character interval) 5 subsequent to the transmission of the character from the next previous sender. The time intervals between successive transmissions of a character are not fixe-d nor necessarily uniform in length and may be adjusted to suit prevailing conditions in the transmitting medium. Without limiting the scope of the invention but to simplify the description thereof, it will be assumed that signals will be transmitted three times, requiring three control senders, although in practice any l5 number of such senders may be used, with increasing accuracy of reception as the number of repetitions increases. The control senders may be connected directly to the transmitting medium or indirectly through a master sender.

The type of receiving mechanism herein described takes the characters as they are received and records them in order by perforating a tape. The tape passes through three senders so spaced on the tape that they pick up simultaneously the repetitions of each character. Indications sent by these senders are combined for each character element to make a single element (for the printer mechanism) which represents the majority vote of the senders on the element. Thus an element may have one of its three transmissions mutilated and recorded as an error on the tape without causing an error in the printer. When transmission is repeated more than twice7 more errors, of course, would be allowable.

Referring to the diagrams: Figure 1 is a schematic diagram of a type of apparatus suitable for controlling printing telegraph impulses sent from a radiotelegraph transmitting station, Fig. 2 is a schematic diagram of apparatus suitable for controlling the printing of the characters by the receiving telegraph printer after the characters which were received from the transmitting station have been recorded in the order received on the receiving tape, and Fig. 3 is a schematic diagram of a modification of the invention which eliminates signals known to` be in error because of fading or heavy static.

In Fig. 1, I is a standard teletypewriter (telegraph printer) which makes perforations 2 on tape 3 in accordance with the 5-unit code for the characters to be transmitted by radio to the receiving printer. l may be a keyboard perforator, such, for example, asthat shown in the patent to Krum, No. 1,884,753, or a reperforator such, for

example, as that shown in the patent to Kleinschmidt, No. 1,884,743, the latter being used where the signals are previously transmitted over a circuit and are received at the station shown in Fig. 1. Sender contacts 4, 4 are aligned with the rows of perforations 2 so that electrical contact is made through each perforation and is broken where no perforation exists. The contacts 4, 4 may, for example, be those shown in the patent to Benjamin, No. 1,298,440. Similar operations are performed by sender contacts 5, 5, and 6, 6 which are spaced from contacts 4, 4 by (1i-1) and (m-l-n-l) intervening characters, respectively, on tape 3, (m) and (n) being any assigned integers. Numbering characters from right to left, if contacts 6, 6 are on character 51:, contacts 5, 5 are on character (fr-l-m) and contacts 4, 4 are on character (zc-i-m-f-n) Motor 1 drives brush 8 and gear 9 which meshes with pinion I9, having a 1-3 ratio with gear 9. Pinion I9 drives brush II of selector I2 over segments I3 (start), I4, I5, I6, I1, I8 and I9 (stop) so arranged that the printer impulses are of proper duration. Segments 28, 2| and 22 of distributor 23 are of such length as to be traversed by brush 8 while brush II is traversing segments I4, I5, I6, I1 and I8. Segments 24, 25 and 26 are of such length as to be traversed by brush 8 while brush I I is traversing segments I9 and I3. One small segment and one large segment together cover 120 (in the case of 3 senders), because brush II makes 3 revolutions to 1 revolution of brush 8.

While brush 8 is on segment 29 and contacts 4, 4 are on character (-l-m-l-n), battery 21 is connected through lead 28, brush 8, segment 29 and lead 29 to sender` contacts 4, 4. If 5 perforations appear on the tape under contacts 4, 4, battery is connected through the contacts to buses 3D, 3|, 32, 33 and 34, which in turn are connected respectively to segments I4, I5, I6, I1, and I8 on selector I2. If any of the ve positions for perforations are not perforated, the corresponding buses and segments do not have the battery connection. While brush II is traversing a segment which has battery connection, current from battery 21 goes through the circuit established to the segment, through brush I I, lead 35 and relay 36, which, now being energized, closes contacts 31 and causes a marking pulse to be sent to the transmission system 38. While brush II is traversing a segment which has no battery connection, a space impulse is sent to the transmission system 38 by the closing of contacts 39.

The radio transmitter 38 may be of any type that is capable of translating marking and spacing impulses into suitable radio telegraph signals, which may be of any Wave length or lengths. The said signals are impressed on the associated antenna for transmission therefrom.

When brush 8 leaves segment 20 and is traversing segment 24, battery 21 is connected through leads 28 and 40 to segment I9, thereby causing, when brush II is on segment I9, relay 35 to be energized and close contacts 31, whereupon a marking impulse is transmitted from radio transmitter 38. When brush II is on segment I3, which has no battery connection at any time, a space impulse is sent out by transmission system 38. The spacing impulse from segment I3 and the marking impulse from segment I9 constitute the start and stop impulses for synchronizing the transmitting printer with the receiving tape cutter by the ordinary start-stop method. Obviously any other well-known method of synchronizing the transmitter driving motor 1 and the tape cutter 5D of Fig. 2 could be employed.

After brush 8 has passed over segment 20 all the segments from I3 to I8, inclusive, have been passed over by brush II, and it is then on segment I9. Brush 8 then passes over segment 24, establishing a connection from battery 21, through lead 28, brush 8, segment 24 and lead 4I to magnet 42 which causes the tape 3 at contacts 4, 4 to step forward to the next character (-i-m-I-n-l-l) and stop in accordance with the operation of well known tape sender devices.

Brush 8 is then moved on to segment 2 I, where the operations described for segment 29 are repeated, except that character (at-i-m) is undergoing transmission through lead 43 and contacts 5, 5. Likewise, when brush 8 reaches segment 25, current passes through lead 44 and magnet 45, which steps tape 3 to character (af-i-m-i-l).

Character (m) is transmitted through segment' 22, lead 46 and contacts 6, 6. Current through brush 8, segment 23, lead 41 and magnet 48 causes the tape to step to character (zc-l-l), whereupon the cycle of transmission begins again on character (at-l-m-l-n-l-l), through contacts The order of transmission of. characters would be zu, :1I-71., .r-n-m, .r-i-l, :v -n+1, -n-m-i-l, 324-2, m-n-l-Z, m-n-m|2, 3:-1-n, -m, .r-f-n-l-l, 03+1, :r-m-i-l, -l-m, -i-m-n, -n at-l-m-i-n, -l-m, sc, .'r-l-m-l-n-i-l, -l-m-l-l, :r-l-l, .'r-l-m-l-n-f-Z, .r-i-m-l-2, :r4-2, etc. It becomes evident then, that a given character which appears initially at :c appears second as the order of transmission and reception. Such spacing is illustrated in the scheme in Fig. 2.

At the receiving station, shown in Fig. 2, the impulses are picked up by the radio receiver 49, which may be of any type suitably designed to receive the Signals sent by transmitter 38 and to translate those signals into their equivalent marking and spacing impulses which are amplied and relayed to the tape reperforator 5D. This may be of any type well known in the art, such, for example, as that shown in the patent to Kleinschmidt No. 1,884,743, which is of the startstop type. That reperforator cuts perforations 5I in the tape 52, according to the way the receiver 49 receives the transmitted impulses, with or without errors due to interference mutilation. While the invention has been disclosed as embodied in a start-stop system it is not so limited but may be equallyl well employed in a synchronous system, in which case the reperforator would be of the type Shown, for example, in the patent to Krum et al. No. 1,174,427. The tape 52 passes through three senders so spaced that they simultaneously pick up the repetitions of the characters. Those devices may be of the type heretofore referred to in describing the transmitting station, as disclosed, for example, in the patent to Benjamin, No. 1,298,449. Thus since character of Fig. 1 was transmitted again as character @+En-1 1) and (-l-3(m+1L)-i2), it appears rst as character (y) on the receiving tape 52, Where the characters are numbered from right to left, next as character (y-l-Bn-f-l), third as character (y+3(m+11.) +2) Battery 53 is connected by leads 54 and 55 to resistances 56, 51 and 58 which are in series, respectively, with sender contacts (59, 59), (S0, B0) and (6I, GI). These contacts are connected b y buses 62, 63, 64, and 66 to relays 61, 68, 69, 10 and 1I, respectively, which require current from at least two senders to make them operate and close contacts 12, 13, 14, 15 or 16, respectively. Resistances 56, 51 and 58 are of such value that current passing through only one resistance will not operate a relay. As long as two transmissions of. a character element (5 elements per character) were received correctly, the element will be recorded correctly. If the character element sent was a blank, and two blanks and one perforation are received the current resulting from the contact through the single perforation will be insuicient to operate the relay and a blank will be registered by the relay. On the other hand if the character element sent was a perforation and one blank is received the current resulting from the contacts through the twoperforations will be suicient to operate the relay and a perforation will be registered.

From battery 53, connection is made through relay 11 and lead 18 to selector brush 19, which, driven by motor 8i), wipes segments 8| (start), 82, 83, 84, 85, 86 and 81 (stop) in turn. This selector system 98 is substantially identical with that of l2 in Fig. l and is adapted to transmit start-stop printer signals to the recording device 89 which may be a reperforator like 50, shown in the patent to Kleinschmidt, No. 1,884,743, or a standard receiving teletypewriter. When current flows through relay 11, contacts 88 are closed, causing a marking impulse to be sent to printer 89. When rela-y 11 is not operated, space impulses are sent through contacts 90 to the printer. Current will ow through rrelay 11 only when brush 19 is grounded through segment 82, 83, 84, 85 or 88; lead 9|, 92, 93, 94 or 95 and Contact 12, 13, 14, 15 or 18, respectively, or through segment 81, lead 98 and relay 91. Thus, selector 98 causes the marking and space impulses to be sent to the printer in accordance with the majority vote of the multipled perforations on the tape. While brush 19 is on segment 81, current flowing through relay 91 operates the relay which closes contacts 99 and connects battery 53 through lead 54, contacts 99 and lead 90 to stepping magnets li, |82 and |93. All three magnets Operate simultaneously and cause the tape to advance three characters at each sender.

When, during a fade out or during a heavy static impulse, the signal to noise ratio is so poor that the received signals are likely t0 be entirely incorrect when recorded on tape 5I it evidently would be better to throw out such signals from the combining process. A modification of the invention including this feature is illustrated by Fig. 3, which shows a radio receiver 49a and an automatic tape perforator 58a, which are broadly similar to those devices shown in Fig. 2 at 49 and 50, respectively, but also, are capable of performing additional functions. The automatic gain control circuit |84 of the receiver is brought out to include relay |85 arranged to break five contacts |86 when current above a certain value ows in its winding and to make these iive contacts when the current in the winding falls below a certain value. The automatic gain control is assumed to be of the well known type, such as is shown in the patent to Friis, No. 1,675,848,

which is shown schematically in Fig. 4 of the v drawings. In the circuit of that figure, in which the same symbols have been' used as in the patent to designate corresponding parts, the rectified sign-al current is passed through the resistance I8, the drop of potential across which is used as grid bias for the amplifier tubes, such as tube 3, thereby changing the gain to maintain substantially constant signal output. 'The circuit I 04 carries this rectified signal current through the relay |85 which may be in series with the battery l1, coil I9 and the plate'lament path of rectifier I6 as shown in the aforesaid patent to Friis. When signals become weak this rectied current falls off, the control ceases to maintain constant signal output and the signals become unreliable. In the present arrangement the relay |85 is adjusted to release its armature at the reduced cur,- rent corresponding approximately to this gain control limit. The ve contacts are then made and current from battery |01 is caused to flow to the ve magnets |88. These five magnets in the tape cutter are those which operate in response to received signals to control respectively the cutting of the five holes in the tape. In the tape cutters of this Well known type, when cur'- rent ows in any magnet a corresponding hole is punched in the tape. It is evident that as long as relay |95 is released and contacts |06 are made ve holes will be punched in the tape for each character no matter what code signal is received. In the printer code, five holes represent a blank or an erasure rather than a letter or othercharacter.

It is now assumed that the tape 5Ia is fed to a combining and recording system identical with that to which tape 5| is fed in Fig. 2 with the exception that four senders are employed instead of three. In other words it is a quadruple system rather than a triple system. Also the relays 61--1I, inclusive, are adjusted so that current through three sender contacts rather than two is required to operate them. It is further assumed that the transmitting system is a quadruple one and the characters are sent four times at intervals rather than three times.

The functioning of such an arrangement is as follows: When signals are strong the relay |05 remains operated and the system functions just Cil like the triple system already described except that it is a four-element system rather than a three. If signals become so weak as to release relay |95, rows of five holes representing blanks i' will be punched on the tape instead of received code combinations until the signals again become strong. As these perforations pass under a sender element such as 56, contact is made on al1 Y ve contactors and one current element is sent i maining three senders of the quadruple system will govern the choice of character recorded by the indicator 89 on a two out of three basis. That is, when signals are good the apparatus will function as a three out of four system and when signals are lost it will function as a two out of three system. In other words, the apparatus automatically rejects the evidence from signals known to be in error and uses only the remaining evidence.

Strong static impulses usually produce errors in ordinary systems by causing all five holes to be punched. In this system such errors are automatically rejected and the effect of strong static is thereby mitigated.

Other methods of repeating, recording and interpreting the signals could -be employed without departing from the novel principles herein disclosed. For example, the perforated tapes and the plurality of senders could be replaced by phonograph records or the wire of a telegraphone employing a plurality of spaced pickup devices, the signals being sent and received as audible tones. Also the application of the invention is not limited to printing telegraphy, since any form of record capable of being conveyed by telegraphic type signals may be employed, such for example, as tape sending and curve drawing tape recording. Also the invention may be applied to facsimile and picture transmission, particularly those forms in which the image is built up of individual black and White elements transmitted by telegraphic type signals.

What is claimed is:

1. A mark and space signal transmitter adapted to send code groups of signals repeatedly, a transmitting medium through which said signals are sent, said medium introducing variations in signal strength, a receiver for said signals, means for storing received signals, means for combining stored signals corresponding to the repeated sending of each code group, means for indicating the result of said combination, and means connected to the said receiver and responsive to a predetermined drop in signal strength to automatically produce upon said storing means a clear-out signal Whenever any impulse of a received signal falls below a prefixed level.

2. In a signaling system for mark and space signals the combination with means for sending each code group of signal elements a plurality of successive times separated by time intervals not all of equal length during which intervals other code groups are sent, a transmitting rnedium, means for receiving said signals including automatic means for summing the elects produced by the reception of the several repetitions of each signal and means for indicating the code combinations identied by such summation.

3. In a signaling system for mark and space code signals the combination with means for sending each signal element a plurality of successive times separated by time intervals not all of equal length during which one or more code combinations of signal elements is sent, a transmitting medium, receiving means including means for storing the received eiects, means for automatically comparing said received eiects to choose therefrom a majority effect and means for indicating the said majority effect.

4. Means as in claim 3 wherein the said sending means is adapted to permit alteration of the lengths of said time intervals.

5. A receiving system for mark and space signals sent in repeated code groups comprising means for receiving signals, means for recording the said received signals, the said recording means including storage means upon which a. record is made, means for combining the stored signals corresponding to the repetitions of each code group, means for indicating the result f each such combination of stored signals corresponding to the said repetitions, means associated with said receiving means and responsive to the strength of the received signals and operative upon said means for recording to produce upon the said storage means a positive clear-out symbol, Whenever the strength of any impulse of a code group falls below a predetermined value, which symbol indicates that the said signal is erroneous.

6. In a radiotelegraph system, the method of avoiding errors due to fading and noise which comprises sending more than once the signals corresponding to every character of a message, receiving the said signals, recording the signals received above a predetermined value of signal strength creating a characteristic record upon the recording means Whenever any signal impulse falls below a predetermined value, which characteristic record is in substitution for the signal character then being received, combining all records corresponding to the several sendings of each character of the said message, and producing the message corresponding to the combined records.

'7. A receiving system for mark and space signals sent in repeated code groups, each group consisting of a plurality of impulses, comprising means for receiving such signals, means for recording such received signals, the said recording means including means for storing the signals as received, means for effectively combining the signals of each code group, means for indicating the resultant signals of each group as thus stored, and a relay adjusted to respond Whenever the strength of a signal impulse falls below a prefixed limit to impress upon said storage means a characteristic symbol in substitution for the record of the code group that would have been recorded if such diminution in signal strength had not occurred.

RALPH BOWN. 

